Smoking articles, particularly cigarettes, generally comprise a tobacco rod of shredded tobacco (usually, in cut filler form) surrounded by a paper wrapper, and a cylindrical filter aligned in an end-to-end relationship with the tobacco rod. Typically, the filter includes a plug of cellulose acetate tow attached to the tobacco rod by tipping paper. Ventilation of mainstream smoke is achieved with a row or rows of perforations about a location along the filter. Such ventilation provides dilution of drawn mainstream smoke with ambient air to reduce the delivery of tar.
Particulate efficiency of a filter is typically resolved as the level of tar into a filter minus tar level out of the filter divided by the tar level into the filter. Ventilation tends to lower particulate efficiency of a filter.
Upon lighting a cigarette, a smoker draws mainstream smoke from the coal at the lit end of the cigarette. The drawn cigarette smoke first enters the upstream end portion of the filter and then passes through the downstream portion adjacent the buccal (mouth) end of the cigarette.
Mainstream smoke from carbon filters tend to have a flavor note that is contrary to consumer preferences, and that therefore their employment in commercially offered cigarettes has not been heretofore widespread.
It would be desirable to provide a cigarette having a cigarette filter incorporating a sorbent such as carbon and/or other materials capable of absorbing and/or adsorbing gas phase constituents present in mainstream cigarette smoke, while providing favorable absorption/adsorption, dilution and drawing characteristics, and adding flavor to the filtered smoke so as to enhance consumer acceptability.
Furthermore, it would be desirable to provide such a filter with desirable residence time in the adsorbent/absorbent-containing region while simultaneously achieving a pressure drop downstream of the dilution region and the adsorbent/absorbent so as to provide acceptable drawing characteristics of puffs of smoke having reduced gas phase constituents but with acceptable taste and resistance-to-draw.